This invention relates to a protective barrier for the protection of marine works, and in particular the problem of protection of marine works of large dimensions. It also relates to a method of installation of the protective barrier.
Means of protection are presently used for works on the sea coast or in river beds, such as coffer-dams consisting of sheet piles or of concrete structural elements, possibly assembled in watertight manner providing a zone sheltered from the currents and/or the waves.
These existing means are either of a temporary character, such as those used in the case of repairs or construction of elements of works anchored at the sea/river bed and generally enclose a relatively small surface; or else are of a permanent character such as jetty protection works which take the form of a wall supported by a solid embankment.
Such existing means are generally used only in depths of water less than some thirty meters. Beyond this depth, and for depths corresponding to those of the continental shelf (of the order of 200 m), it is necessary to adopt techniques akin to those of "off-shore" construction. In the latter case the means of protection form part of the main construction and are constructed at the same time as the work element or elements to be protected (e.g. piled or gravity structure intended to support the deck). Such a means of protection is described in French Patent No. 2,277,940, for example, and takes the form of a perforated circular wall integral with the slab and continuing above the water level so as to protect the hollow central tank from the waves and/or impact by floating bodies. The deck rests upon the central tank and columns provided on the top of the perforated wall at a height such that the facilities which it supports are beyond the reach of the highest waves.
The supporting structures of an offshore platform are normally dimensioned to withstand external loads such as those due to waves, wind, current, impacts by ships, ice forces, iceberg impacts, and for a definite period of service. During the course of this period of service, the environmental conditions may change, for example, an increase in the service period, modification of the loading conditions, increase in the water depth due to subsidence of the sea bed upon which the structure rests, or the reuse of the structure on another site, etc. These changes currently necessitate major modification works which may involve long-term stoppages of production/facilities and operations.
This invention aims at dissociating the functions of withstanding external environmental load from those of operating the production facilities, so as to permit installation of modifications without disturbing the operation of original platform/facilities.
The protective barrier, according to the invention, is characterized by the fact that it consists of an enclosure extending from the sea bed to a chosen height above the sea level, surrounding the work to be protected, consisting of at least two parts capable of being assembled along their vertical sides, each of the parts being constructed in the form of a ballastable cellular floating structure.
The explanations and figures given below by way of example will show clearly how the invention may be embodied.